Image forming apparatus

Abstract

An image forming apparatus includes a first medium scanned with a first signal, a second medium scanned with a second signal, a rotary polygon mirror that deflects the first and second signals, a synchronization signal generation circuit that generates a synchronization signal representing a time to start scanning the first medium, and at least one pseudo synchronization signal generation circuit that generates a pseudo synchronization signal with the synchronization signal. The pseudo synchronization signal represents a time to start scanning the second medium. Based on a previously calculated period of the synchronization signal and a period of the synchronization signal counted on a particular surface of the polygon mirror, the pseudo synchronization signal generation circuit generates a particular value for generating the pseudo synchronization signal. Based on the particular value, the pseudo synchronization signal generation circuit starts generating the pseudo synchronization signal when the synchronization signal is enabled.

The invention claimed is: 
     
       1. An image forming apparatus comprising:
 a first scanned medium configured to be scanned with a first optical signal based on first image data; 
 a second scanned medium configured to be scanned with a second optical signal based on second image data; 
 a rotary polygon mirror configured to deflect the first optical signal and the second optical signal; 
 a synchronization detection signal generation circuit configured to generate a synchronization detection signal representing a first scanning start time to start scanning the first scanned medium; and 
 at least one pseudo synchronization detection signal generation circuit configured to generate a pseudo synchronization detection signal with the synchronization detection signal, the pseudo synchronization detection signal representing a second scanning start time to start scanning the second scanned medium, 
 the at least one pseudo synchronization detection signal generation circuit being configured to
 based on a previously calculated period of the synchronization detection signal and a period of the synchronization detection signal counted on a particular surface of the rotary polygon mirror, generate a particular value for generating the pseudo synchronization detection signal, and 
 based on the generated particular value, starts generating the pseudo synchronization detection signal at a time at which the synchronization detection signal is enabled. 
 
 
     
     
       2. The image forming apparatus of  claim 1 , wherein at the time at which the synchronization detection signal is enabled, the at least one pseudo synchronization detection signal generation circuit starts generating the pseudo synchronization detection signal to generate the pseudo synchronization detection signal after the particular surface of the rotary polygon mirror makes one revolution. 
     
     
       3. The image forming apparatus of  claim 1 , wherein the at least one pseudo synchronization detection signal generation circuit includes
 a first counter configured to count the period of the synchronization detection signal, and 
 an arithmetic circuit configured to calculate the particular value based on the previously calculated period of the synchronization detection signal and the period of the synchronization detection signal counted by the first counter. 
 
     
     
       4. The image forming apparatus of  claim 3 , wherein the at least one pseudo synchronization detection signal generation circuit further includes
 a clock oscillator configured to oscillate a count clock signal for operating the first counter based on the particular value calculated by the arithmetic circuit, and 
 a second counter configured to count up to a certain value with the count clock signal oscillated by the clock oscillator to generate the pseudo synchronization detection signal. 
 
     
     
       5. The image forming apparatus of  claim 4 , wherein the arithmetic circuit calculates a frequency division ratio for dividing a frequency of the count clock signal based on the particular value and a previously calculated frequency division ratio for dividing a frequency of a source oscillation clock signal supplied to the clock oscillator. 
     
     
       6. The image forming apparatus of  claim 4 , wherein the arithmetic circuit calculates a target value for generating the pseudo synchronization detection signal based on the particular value and a previously calculated target value for generating the pseudo synchronization detection signal, the previously calculated target value being counted by the second counter. 
     
     
       7. The image forming apparatus of  claim 1 , wherein the rotary polygon mirror includes a plurality of surfaces, and
 wherein the at least one pseudo synchronization detection signal generation circuit includes a plurality of pseudo synchronization detection signal generation circuits corresponding to the plurality of surfaces of the rotary polygon mirror. 
 
     
     
       8. The image forming apparatus of  claim 7 , wherein each of the plurality of pseudo synchronization detection signal generation circuits generates the pseudo synchronization detection signal for a corresponding one of the plurality of surfaces of the rotary polygon mirror. 
     
     
       9. An image forming apparatus comprising:
 a first scanned medium that is scanned with a first optical signal based on first image data; 
 a second scanned medium that is scanned with a second optical signal based on second image data; 
 deflecting means for deflecting the first optical signal and the second optical signal; 
 synchronization detection signal generation means for generating a synchronization detection signal representing a first scanning start time to start scanning the first scanned medium; and 
 pseudo synchronization detection signal generation means for generating a pseudo synchronization detection signal with the synchronization detection signal, the pseudo synchronization detection signal representing a second scanning start time to start scanning the second scanned medium, 
 the pseudo synchronization detection signal generation means
 based on a previously calculated period of the synchronization detection signal and a period of the synchronization detection signal counted on a particular surface of the deflecting means, generating a particular value for generating the pseudo synchronization detection signal, and 
 based on the generated particular value, starting generating the pseudo synchronization detection signal at a time at which the synchronization detection signal is enabled. 
 
 
     
     
       10. The image forming apparatus of  claim 9 , wherein at the time at which the synchronization detection signal is enabled, the pseudo synchronization detection signal generation means starts generating the pseudo synchronization detection signal to generate the pseudo synchronization detection signal after the particular surface of the deflecting means makes one revolution. 
     
     
       11. The image forming apparatus of  claim 9 , wherein the pseudo synchronization detection signal generation means includes
 first counting means for counting the period of the synchronization detection signal, and 
 arithmetic means for calculating the particular value based on the previously calculated period of the synchronization detection signal and the period of the synchronization detection signal counted by the first counting means. 
 
     
     
       12. The image forming apparatus of  claim 11 , wherein the pseudo synchronization detection signal generation means further includes
 clock oscillating means for oscillating a count clock signal for operating the first counting means based on the calculated particular value, and 
 second counting means for counting up to a certain value with the oscillated count clock signal. 
 
     
     
       13. The image forming apparatus of  claim 12 , wherein the arithmetic means calculates a frequency division ratio for dividing a frequency of the count clock signal based on the particular value and a previously calculated frequency division ratio for dividing a frequency of a source oscillation clock signal supplied to the clock oscillating means. 
     
     
       14. The image forming apparatus of  claim 12 , wherein the arithmetic means calculates a target value for generating the pseudo synchronization detection signal based on the particular value and a previously calculated target value for generating the pseudo synchronization detection signal, the previously calculated target value being counted with the second counting means. 
     
     
       15. The image forming apparatus of  claim 9 , wherein the deflecting means includes a plurality of surfaces, and
 wherein the pseudo synchronization detection signal generation means is provided for each of the plurality of surfaces of the deflecting means. 
 
     
     
       16. The image forming apparatus of  claim 15 , wherein the pseudo synchronization detection signal generation means generates the pseudo synchronization detection signal in accordance with the each of the plurality of surfaces of the deflecting means.